Fluorine-containing polymers (i.e., fluoropolymers or fluorinated polymers) are a commercially important class of materials. Many fluoropolymers are known to exhibit high thermal stability and usefulness at high temperatures as well as extreme toughness and flexibility at very low temperatures. Many fluoropolymers are also almost totally insoluble in a wide variety of organic solvents and resistant to many chemical compounds that might degrade other classes of less resistant materials. Additionally, many fluoropolymers are recognized for their barrier properties; i.e., their ability to prevent the passage of liquids or vapors.
Increased concerns with evaporative fuel standards have led to a need for fuel system components that have improved barrier properties to minimize the permeation of fuel vapors through automotive components such as fuel filler lines, fuel supply lines, fuel tanks, and other components of automobile emission control systems. Multi-layer articles such as multi-layer tubing have been used within these applications. These multi-layer products can comprise a fluoropolymer, which provides an inert vapor barrier, and one or more other layers that can add strength, rigidity, or other mechanical properties to the multi-layer article. As an example, some multi-layer articles include a fluoropolymer and a layer comprising a substantially non-fluorinated polymer.
To be most useful, these multi-layer articles should not delaminate during use. That is, the adhesive bond strength between the different layers of the multi-layer article should be sufficiently strong and stable so as to prevent the different layers from separating on exposure to, for example, fuel, emission fluids, caustic or acidic solutions, or other aggressive chemicals. However, poor adhesion between two very dissimilar materials, fluoropolymer and hydrocarbon polymer, makes the formation of these desired constructions difficult.
A variety of methods have been employed to bond polymeric materials comprising a fluoropolymer to substantially non-fluorinated polymeric materials. For example, the layers can be adhesively bonded together by a layer of adhesive material between the two layers. Alternatively, surface treatment of one or both of the layers, used independently or in conjunction with adhesive materials, has been used to bond the two types of materials together. For example, layers comprising a fluoropolymer have been treated with a charged gaseous atmosphere followed by lamination with a layer of thermoplastic polyamide. As another approach, “tie-layers” have been used to bond a fluoropolymer material to a layer of material comprising a substantially non-fluorinated polymer. The tie layer was a layer comprising a blend of dissimilar materials disposed between the fluoropolymer and substantially non-fluoropolymer layers. Some of the disadvantages of known tie layer materials include loss of desirable physical properties of the base polymer of the tie layer, the additional manufacturing steps necessitated by the use of a “tie layer,” and other problems associated with handling some of the ingredients used in the tie layers.